The subject invention relates to sheet accumulators. Note particularly it relates to a method and apparatus for accumulating sheets of a material such as paper having various sizes in a stack.
It is known to be desirable in the paper handling art to provide paper handling apparatus with mechanisms, known as accumulators, which accumulate a sequence of sheets being processed by the apparatus to form a stack, or accumulation, for further processing. For example, a sequence of sheets might be fed to a printer for printing of predetermined information, and the output of the printer fed to an accumulator where a predetermined number of sheets in the sequence would be accumulated, and the resulting accumulation passed on for further processing, such as folding and insertion into an envelope.
FIG. 1 shows a schematic representation of a typical prior art accumulator 10. A pair of feed rollers 12 feeds a sheet onto a guide 14. The nip of rollers 12 is offset from guide 14 by an amount O so that the trailing edge of one sheet does not interfere with the next leading edge when the next sheet is fed. Urge rollers 16 maybe provided to assure that the sheet moves along guide 14 until it reaches rollers 18. (By urge rollers herein is meant rollers designed to apply a limited force to a sheet so that the rollers will slip before the sheet buckles.) Rollers 18 are stopped, or may be counter-rotating, to provide a stop to halt the movement of the sheet along guide 14. As successive sheets are fed by rollers 12 they are positioned, because of offset O, on top of the previous sheets and are driven by rollers 16 against the nip of rollers 18 to form the accumulation. (Alternatively offset O may be replaced with a step in guide 14 to provide relief so that the trailing and leading edges of successive sheets do not interfere, and alternative mechanisms may be used in place of rollers 18 to stop the sheets and form the accumulation; for example a movable gate which is activated to stop the sheets and displaced to allow the accumulation to move on for further processing.)
Such accumulators are well known and generally function satisfactorily for their intended purpose. One disadvantage of such accumulators is, however, that the length of the sheets to be accumulated must be approximately equal to L, the distance from rollers 12 to rollers 18. Consideration of FIG. 1 quickly shows that a sheet which is substantially shorter than L might interfere with the leading edge of the next sheet, despite offset O. Conversely, a sheet which is substantially longer than L might obstruct, or even fail to clear entirely, the nip of rollers 12. At most a single, last, shorter sheet might be included with the accumulation. If a number of shorter sheets were desired a second feed mechanism 20, including second feed rollers 22 second guide 26, and second urge rollers 28 would have to be provided. Of course, for the reasons just discussed, the length of these shorter sheets would necessarily be approximately l. And, as can be seen from consideration of FIG. 1 the shorter sheets would, necessarily, be placed on top of the longer sheets fed by rollers 12. Further, it can readily be imagined how rapidly the complexity of, and space required for, an accumulator such as accumulator 10 increases as the number of different sized sheets to be accumulated increases.
FIG. 1 is believed to fairly represent prior art accumulators and the difficulties associated therewith, however those skilled in the art will recognize that numerous other configurations for accumulators are known in the prior art, all of which, however, are believed to suffer from the disadvantages described. Those skilled in the art will also recognize that the details of the mechanical design of rollers, or feedbelts, guides and stop gates, etc. as are shown in schematic form in FIG. 1 and the following Figures, are very well known in the art and further discussion of such detailed mechanical design is not believed necessary for an understanding of the subject invention.
Accordingly it is an object of the object invention to provide an accumulator having an increased capacity and flexibility for accumulating sheets of various sizes.